Laser induced reverse transfer for microfabrication

Gurinderpal Singh Dhami, Ryerson University

Date of Award

2009

Degree Type

Thesis

Degree Name

Master of Applied Science (MASc)

Department

Mechanical Engineering

First Advisor

K. Venkatakrishnan

Second Advisor

Bo Tan

Abstract

The general objective of this thesis is to introduce ultrafast "Laser Induced Reverse Transfer" (LIRT) as a technique for material transfer in micro-fabrication. LIRT is performed using femtosecond laser radiation of wavelength 515 nm with gold coated silicon wafers under ambient conditions. The material transfer process is explained by the dynamics of a laser ablated plasma plume. The influence of processing parameters such as laser pulse energy, pulse width and scan speed on the width of transferred material is also investigated. The width of the deposition increases with the increase in pulse energy while it decreases with scan speed. Also, the width increases with laser pulse width ranging from femtosecond to picosecond range. In general the transferred material size is determined by the amount of material present in the plasma plume which depends on the energy deposited in the bulk material by laser irradiation. In the femtosecond pulse width range, the increase in pulse energy at constant pulse width transfers more energy in a short time with minimal heating effect to the surrounding material. Hence, the efficiency of material removal increases. This in turn enhances the feature size. On the other hand, as the laser pulse width increases from femtoseconds to picoseconds, the interaction time of laser radiation with material increases. This leads to an increase in the amount of material removed, thereby increasing the transferred material size, However, thermal damage to the surrounding material increases. An increase in scan speed at constant pulse energy decreases the laser interaction time, which results in a decrease in amount of material in the plasma plume. This in turn decreases the width of the deposited material. In general, femtosecond laser induced reverse material transfer is an efficient technique for microfabrication and can be used for device manufacturing.